The presence of inorganic carbon (as CO.sub.2, HCO.sub.3.sup.-, and CO.sub.3.sup.=) in samples to be anaIyzed for total organic carbon (TOC) creates two adverse affects: a positive interference with the CO.sub.2 detector and a decrease in the oxidation rate of organics. It is desirable to remove inorganic carbon (IC) to allow direct TOC measurement of reclaimed water streams.
Inorganic carbon (IC) as dissolved CO.sub.2 causes positive interference with total organic carbon (TOC) measurements, and as carbonates, inorganic carbon adversely affects oxidation of organics. Therefore, it is desirable to remove inorganic carbon (IC) to allow direct TOC measurement of reclaimed water streams. The most sensitive standardized method of total carbon measurement, with a reported detection limit of 50 ug organic carbon/liter, which is described in STANDARD METHODS FOR THE EXAMINATION OF WATER AND WASTE WATER, 16th Ed. as follows: Inorganic carbon, present in water as carbonate and/or bicarbonate ions above pH 4-5, is converted to CO.sub.2 by addition of aqueous acid (e.g. 10% phosphoric acid). Carbon dioxide is then removed from the sample using an inert gas and carried to a non-dispersive infrared (NDIR) detector to measure CO.sub.2 (hence inorganic carbon concentration). The sample is then subjected to UV-persulfate oxidation; the organic carbon is oxidized to CO.sub.2 and removed using purge gas. The organic carbon concentration is measured as CO.sub.2 in the NDIR detector. This method has significant disadvantages as applied to on-Iine monitoring of waste streams in microgravity. These disadvantages include the requirement for sample acidification to convert carbonate and bicarbonate to CO.sub.2 using an expandable liquid reagent (phosphoric acid). It is also considered disadvantageous to use expandable aqueous persulfate solutions in the Space Station Freedom (SSF) environment because of the weight limitations thereof. Further, transfer of inorganic carbon as CO.sub.2 out of the sample using purge gas is a gravity-dependent process which, of course, can be non-functional in the microgravity of the SSF environment. It is therefore considered desirable to provide a reliable gravity independent process for total organic carbon and total inorganic carbon measurement. More specifically, it is considered desirable to provide a reagentless inorganic carbon separator which includes a solid-phase acid module integrated with a CO.sub.2 -permeable degasser. It is also considered desirable to provide a passive total inorganic carbon (TIC) removal module containing a CO.sub.2 adsorbent. The module should remove the TIC and fix it in the solid form in a single process step. Even further, it is considered desirable to provide solid-phase TOC and TIC functional check modules to provide a means of verifying instrument performance without storage of unstable liquid reagents.
The water quality monitor (WQM) hardware presently being developed for the Space Station Freedom does not require persulfate reagents, but at present will require addition of liquid acid and uses centrifical gas/liquid separators. It is considered desirable to provide an alternative to the use of liquid-phase acid reagents such as phosphoric acid and to provide a suitable alternative for the present requirement for purge gas such as nitrogen for removaI of dissolved CO.sub.2 from water. Further, from the standpoint of use in orbital environments such as space stations and for other interpIanetary activities, it is considered desirable to provide a solid-phase system for removal of CO.sub.2 without using a purge gas. It is also considered desirable to provide for conversion of carbonate and bicarbonate to CO.sub.2 without the addition of an expendable liquid reagent such as phosphoric acid. This would permit elimination of corrosive liquid acids in the space station or space-craft environment.